1. Field of the Invention
The present invention broadly relates to a medium- or low-speed diesel engine which operates with a gas fuel and, more particularly, to a device for preventing abnormal flow of fuel from a gas fuel injector of such a diesel engine.
2. Description of the Related Art
In operation of a gas fuel diesel engine, a gas injector operates to inject a gas fuel into cylinders in synchronism with the combustion cycles in these cylinders. The rate of injection of the gas fuel is controlled by a gas fuel controller. The gas injector has a valve which is connected to and operated by a spindle so as to open and close the passage through which the gas fuel is injected. This known gas injector, however, involves a risk of stick of the spindle due to, for example, jamming of foreign matters, with a result that the valve is kept opened regardless of the combustion cycle so that a large quantity of gas fuel reaches the exhaust pipe of the engine through the cylinder. In consequence, the concentration of the gas fuel in the exhaust pipe is increased to cause an explosion in the exhaust pipe. Such an explosion may seriously damage the diesel engine.
In order to obviate this problem, it has been proposed to limit the maximum flow rate of the gas fuel by an orifice provided in the main pipe of the gas fuel. The cross-sectional area of the orifice port is selected to be slightly greater than that corresponding to the fuel injection rate corresponding to the maximum load per cylinder. This proposal, however, is still unsatisfactory in that, in the event of a stick of the gas injector while the engine is operating at a comparatively low load level, the gas fuel is injected at the rate corresponding to the maximum load level, whereas the flow rate of the intake air is controlled in accordance with the load level, so that the concentration of the fuel in the exhaust pipe is increased beyond the explosion limit, causing a risk of an explosion in the exhaust pipe.